Freshwater Snail Lymnaea Research Articles

Molluscicidal activity of Sapindus mukorossi and Terminalia chebula against the freshwater snail Lymnaea acuminata

The molluscicidal activity of Sapindus mukorossi and Terminalia chebula fruit powder against the vector snail Lymnaea acuminata was time and concentration dependent. The molluscicidal activity of T. chebula fruit powder (96 h LC 50:93.59 mg L −1) was more pronounced than that of S. mukorossi fruit powder (96 h LC 50:119.57 mg L −1). Ethanolic extracts of S. mukorossi and T. chebula fruit powder were more toxic than their other organic solvent extracts. The molluscicidal activity of ethanolic extract of S. mukorossi fruit powder (24 h LC 50:2.75 mg L −1) was more effective than the ethanolic extract of T. chebula fruit powder (24 h LC 50:124.06 mg L −1). The 96 h LC 50 of column-purified fraction of S. mukorossi fruit powder was 5.43 mg L −1 whereas those of T. chebula fruit powder was 7.49 mg L −1. Column, thin layer and high performance liquid chromatography analysis demonstrates that the active molluscicidal component in S. mukorossi and T. chebula is saponin (96 h LC 50:1.31 mg L −1) and tannic acid (96 h LC 50:1.64 mg L −1), respectively. These plants may be used as potent source of molluscicides against the snail L. acuminata.

Low environmental calcium blocks long-term memory formation in a freshwater pulmonate snail

The freshwater snail Lymnaea stagnalis (L.) is considered a calciphile and exhibits reduced growth and survival in environments containing less than 20mg/l environmental calcium. Although it has no apparent effect on survival at 20mg/l, reducing environmental calcium increases metabolic demand, and as such we consider that this level of calcium acts as a stressor on the snail. We exposed snails to acute periods of low environmental calcium and tested their ability to form intermediate-term memory (ITM) and long-term memory (LTM) following one trial operant conditioning (1TT) to reduce aerial respiratory activity in hypoxic conditions. We also assessed whether there were changes in the electrophysiological properties of a single neuron, right pedal dorsal 1 (RPeD1), which has been demonstrated to be necessary for LTM formation. Following training in high (80mg/l) environmental calcium, L. stagnalis formed ITM and LTM lasting 24h and demonstrated a significant reduction in all activity measured from RPeD1; however when snails were exposed to low (20mg/l) environmental calcium they were able to form ITM but not LTM. Although no behavioral LTM was formed, a partial reduction in RPeD1 activtiy measured 24h after training was observed, indicating a residual effect of training. The strong effect that environmental calcium concentration had on physiology and behavior in response to training to reduce aerial respiration in L. stagnalis suggests that it is an element of gastropod husbandry that needs to be carefully considered when studying other traits. This study also indicates that L. stagnalis found naturally in low calcium environments may be less able to adapt to novel stressors than populations found in harder waters.

Is the population genetic structure of complex life cycle parasites determined by the geographic range of the most motile host?

Due to their particular way of life, dispersal of parasites is often mediated by their host's biology. Dispersal distance is relevant for parasites because high degree of dispersal leads to high gene flow, which counters the rate of parasite local adaptation in the host populations. Parasites with complex life cycles need to exploit sequentially more than one host species to complete their life cycle. Most trematode parasites have such complex life cycles involving invertebrate and vertebrate hosts. The spatial scales of invertebrate and vertebrate host populations are often different, which may decrease the probability that the parasite cycles locally in the intermediate host population. We used neutral microsatellite markers to determine genetic structure in Diplostomum pseudospathaceum parasites collected from local populations of freshwater snails (Lymnaea stagnalis). D. pseudospathaceum is a trematode that has two intermediate hosts (snail and fish) and a highly motile definitive host (bird). We found that the parasite population infecting the local snail populations showed no genetic structure over a large geographic range (over 300km). We also did not detect evidence for isolation by distance in the parasite. We conclude that dispersal in the motile definitive host is likely to prevent emergence of local population genetic structure in the parasite. Our results suggest that parasite dispersal in the definitive host may limit local cycling of the parasites in the intermediate host populations.

Development of partial life-cycle experiments to assess the effects of endocrine disruptors on the freshwater gastropod Lymnaea stagnalis: a case-study with vinclozolin

Long-term effects of endocrine disruptors (EDs) on aquatic invertebrates remain difficult to assess, mainly due to the lack of appropriate sensitive toxicity test methods and relevant data analysis procedures. This study aimed at identifying windows of sensitivity to EDs along the life-cycle of the freshwater snail Lymnaea stagnalis, a candidate species for the development of forthcoming test guidelines. Juveniles, sub-adults, young adults and adults were exposed for 21 days to the fungicide vinclozolin (VZ). Survival, growth, onset of reproduction, fertility and fecundity were monitored weekly. Data were analyzed using standard statistical analysis procedures and mixed-effect models. No deleterious effect on survival and growth occurred in snails exposed to VZ at environmentally relevant concentrations. A significant impairment of the male function occurred in young adults, leading to infertility at concentrations exceeding 0.025 μg/L. Furthermore, fecundity was impaired in adults exposed to concentrations exceeding 25 μg/L. Biological responses depended on VZ concentration, exposure duration and on their interaction, leading to complex response patterns. The use of a standard statistical approach to analyze those data led to underestimation of VZ effects on reproduction, whereas effects could reliably be analyzed by mixed-effect models. L. stagnalis may be among the most sensitive invertebrate species to VZ, a 21-day reproduction test allowing the detection of deleterious effects at environmentally relevant concentrations of the fungicide. These results thus reinforce the relevance of L. stagnalis as a good candidate species for the development of guidelines devoted to the risk assessment of EDs.

Trophic transfer of aluminium through an aquatic grazer–omnivore food chain

The potential for trophic transfer of aluminium (Al) was investigated using a grazing detritivore, the freshwater snail Lymnaea stagnalis, and a predator, the signal crayfish Pacifastacus leniusculus. Snails were exposed to either aqueous Al (500 μg l −1) in the presence or absence of an inorganic ligand (phosphate (+P); 500 μg l −1) for 30 days, or kept as unexposed controls. Subcellular partitioning of Al in the snail tissues was characterised using ultracentrifugation. Al content in the soft tissues and the subcellular fractions was measured using inductively coupled plasma atomic emission spectroscopy. Exposed and control snails were fed to individually housed crayfish ( n = 6 per group) over 40 days. Water samples, uneaten snail tissue and faeces were collected throughout the experiment in order to assess the fate of Al. Behavioural toxicity to the crayfish was assessed at four time points, and tissue accumulation of Al in soft tissues was measured following a 2-day depuration period. Snails exposed to Al + P accumulated more Al per snail than those exposed to Al only (291 μg vs 206 μg), and also contained a higher proportion of detoxified Al (in inorganic granules and associated with heat stable proteins) (39% vs 26%). There were no significant differences in behavioural activity between the different groups of crayfish at any time point. Crayfish fed snails exposed to only Al accumulated significant levels of Al in their total soft tissues, compared to controls; crayfish fed Al + P-exposed snails did not, even though concentrations of Al in these snails were higher. The highest concentrations of Al were found in the green gland in both crayfish feeding groups, and the gut and hepatopancreas in crayfish fed Al only exposed snails; all of these were significantly higher than in crayfish fed control snails. There was no significant accumulation of Al in the gills or flexor muscle in any group. At least 17% of trophically available Al in the snail tissues was accumulated by the crayfish. This proportion was similar in both feeding groups but, as the proportion of trophically available Al in the snails exposed to Al + P was lower, this led to lower accumulation in the Al + P crayfish feeding group. This study indicates that in comparison to vertebrates, aquatic invertebrates accumulate a higher proportion of Al via oral ingestion but it does not accumulate in tissues that may pose a threat to human consumers.

Effects of copper on the egg development and hatching of a freshwater pulmonate snail Lymnaea luteola L.

A freshwater invertebrate egg development and hatching toxicity test with an Indian freshwater pulmonate snail, Lymnaea luteola, comprising the following developmental endpoints was described: mortality, development, formation of eyes and foot structure, heart rate, duration of different larval stages, and hatching time. Developmental stages were morula, and at third, fifth, and eighth days; the trochophore, veliger, and hippo larvae, respectively. At the age of about 9th to 11th days after egg laying; more than 95% young snail hatched in control laboratory conditions. To evaluate effects on embryonic development, the pulmonate snail eggs of 24-h old were exposed to a series of nominal copper concentrations. The percentage survival of embryos treated in 10–32 μg l −1 of Cu after 240 h of exposure drops sharply at veliger and hippo stages. All embryos died at 100–320 μg l −1 of Cu within 168 h of exposure at trochophore and early veliger stages. The detected abnormalities were malformation of foot, eyes, thinness and incomplete formation of shell, growth retardation, and slow rotation of embryo within the egg capsule as compared to control embryos. Lethal and sublethal effects in terms of mortality and significant delay in hatching could be found in the 3.2, 5.6 and 10 μg l −1 of Cu concentrations. This species is widely distributed in the Indian subcontinent freshwater reservoirs and more sensitive to Cu than other tested aquatic test organisms; therefore, could be used as a test model of Cu and possibly other pollutants for rapid risk assessment of environmental pollutants. The snail egg embryo bioassay is simple, rapid, highly sensitive, cost-effective, and easy to test under standardized laboratory conditions.

MAINTENANCE OF GENETIC VARIATION IN IMMUNE DEFENSE OF A FRESHWATER SNAIL: ROLE OF ENVIRONMENTAL HETEROGENEITY

Natural populations often show genetic variation in pathogen resistance, which is paradoxal because natural selection is expected to erode genetic variation in fitness-related traits. Several different factors have been suggested to maintain such variation, but their relative importance is still poorly understood. Here we examined if environmental heterogeneity and genetic trade-offs could contribute to the maintenance of genetic variation in immune function of a freshwater snail Lymnaea stagnalis. We assessed the immunocompetence of snails originating from different families and maintained in different feeding treatments (ad libitum feeding, no food) by measuring the density of circulating hemocytes, phenoloxidase activity, and antibacterial activity of snail hemolymph. Food limitation reduced snail immune function, and we found significant among-family variation in hemocyte concentration and PO activity, but not in antibacterial activity. Interestingly, food availability modified the family-level variation observed in PO activity so that the relative immunocompetence of different snail families changed over environmental conditions (G x E interaction). We found no evidence for genetic trade-offs between snail growth and immune defense nor among immune traits. Thus, our findings support the idea that environmental heterogeneity may promote maintenance of genetic variation in immune defense, but also suggest that different immune traits might not respond similarly to environmental variation.

Molluscicidal potential of Lantana indica and Alstonia scholaris plants against freshwater snail Lymnaea acuminata

Molluscicidal potential of Lantana indica and Alstonia scholaris plants against freshwater snail Lymnaea acuminata

Enzyme Inhibition by Molluscicidal Components ofMyristica fragransHoutt. in the Nervous Tissue of SnailLymnaea acuminata

This study was designed to investigate the effects of molluscicidal components of Myristica fragrans Houtt. (Myristicaceae) on certain enzymes in the nervous tissue of freshwater snail Lymnaea acuminata Lamarck (Lymnaeidae). In vivo and in vitro treatments of trimyristin and myristicin (active molluscicidal components of Myristica fragrans Houtt.) significantly inhibited the acetylcholinesterase (AChE), acid and alkaline phosphatase (ACP/ALP) activities in the nervous tissue of Lymnaea acuminata. The inhibition kinetics of these enzymes indicates that both the trimyristin and myristicin caused competitive noncompetitive inhibition of AChE. Trimyristin caused uncompetitive and competitive/noncompetitive inhibitions of ACP and ALP, respectively whereas the myristicin caused competitive and uncompetitive inhibition of ACP and ALP, respectively. Thus results from the present study suggest that inhibition of AChE, ACP, and ALP by trimyristin and myristicin in the snail Lymnaea acuminata may be the cause of the molluscicidal activity of Myristica fragrans.

Cys-Loop receptor ionic channels: Structure, function, and regulation

302 The Cys-loop superfamily constitutes a major class of receptor-operated ion channels. Functional channel module contains five protein subunits, with a signature sequence of 13 residues flanked by covalently bound cysteines, situated between binding and channel domains. In vertebrates, Cys-loop receptors are subdivided into cationand anion-selective channels, corresponding to excitatory receptors activated by acetylcholine (ACh) or serotonin, and inhibitory receptors activated by GABA or glycine. Two recent breakthroughs have accelerated our understanding of the molecular structure of the Cysloop superfamily. First, the discovery of acetylcholinebinding protein (AChBP) from the freshwater snail Lymnaea stagnalis , and the determination of its structure at a resolution of 2.7 A. This stimulated homology modeling of ligand-binding domains using AChBP as the template. Second, electron microscopy of ACh receptors from Torpedo at a resolution of 4 A, which revealed the protein backbone and bulky side chains of the compete receptor protein. Cys-loop receptors are involved in rapid synaptic neuro-muscular and neuro–neuronal communication. The functioning of these channels is regulated via external, intracellular and transmembrane domains. As an example, we have shown that cytoplasmic Ca 2+ leads to rapid potentiation of responses to glycine via Ca 2+ binding protein (CaBP). This mechanism may play an important role in Ca 2+ -dependent modulation of rapid synapses in the nervous system of vertebrate. Cys-Loop Receptor Ionic Channels: Structure, Function, and Regulation

Embryonic rotational behaviour in the pond snail Lymnaea stagnalis: influences of environmental oxygen and development stage

Responses of freshwater organisms to environmental oxygen tensions (PO 2) have focused on adult (i.e. late developmental) stages, yet responses of embryonic stages to changes in environmental PO 2 must also have implications for organismal biology. Here we assess how the rotational behaviour of the freshwater snail Lymnaea stagnalis changes during development in response to conditions of hypoxia and hyperoxia. As rotation rate is linked to gas mixing in the fluid surrounding the embryo, we predicted that it would increase under hypoxic conditions but decrease under hyperoxia. Contrary to predictions, early, veliger stage embryos showed no change in their rotation rate under hyperoxia, and later, hippo stage embryos showed only a marginally significant increase in rotation under these conditions. Predictions for hypoxia were broadly supported, however, with both veliger and hippo stages showing a marked hypoxia-related increase in their rotation rates. There were also subtle differences between developmental stages, with hippos responding at PO 2s (50% air saturation) greater than those required to elicit a similar response in veligers (20% air saturation). Differences between developmental stages also occurred on return to normoxic conditions following hypoxia: rotation in veligers returned to pre-exposure levels, whereas there was a virtual cessation in embryos at the hippo stage, likely the result of overstimulation of oxygen sensors driving ciliary movement in later, more developed embryos. Together, these findings suggest that the spinning activity of L. stagnalis embryos varies depending on environmental PO 2s and developmental stage, increasing during hypoxia to mix capsular contents and maintain a diffusive gradient for oxygen entry into the capsule from the external environment (“stir-bar” theory of embryonic rotational behaviour).

Molluscicidal activity of Saraca asoca and Thuja orientalis against the fresh water snail Lymnaea acuminata

The molluscicidal activity of bark powder of Saraca asoca, leaf powder of Thuja orientalis against the snail Lymnaea acuminata was studied. The molluscicidal activity of all the plant products was found to be both time and concentration dependent. The 96 h LC 50 of T. orientalis leaf powder against L. acuminata was 250.5 mg/l. Ethanol extracts were more toxic than other organic extracts. The ethanol extract of T. orientalis leaf (24 h LC 50: 32.74 mg/l) was more effective than that of S. asoca bark (24 h LC 50: 82.38 mg/l). The 24 h LC 50 of column purified fraction of T. orientalis leaf and S. asoca bark powder was 29.25 and 64.89 mg/l, respectively. Saponin and thujone were identified as active molluscicide components in the bark of S. asoca and leaf of T. orientalis, respectively. The product of S. asoca and T. orientalis may be used as potent molluscicides.

Transcriptome analysis of the central nervous system of the mollusc Lymnaea stagnalis

BackgroundThe freshwater snail Lymnaea stagnalis (L. stagnalis) has served as a successful model for studies in the field of Neuroscience. However, a serious drawback in the molecular analysis of the nervous system of L. stagnalis has been the lack of large-scale genomic or neuronal transcriptome information, thereby limiting the use of this unique model.ResultsIn this study, we report 7,712 distinct EST sequences (median length: 847 nucleotides) of a normalized L. stagnalis central nervous system (CNS) cDNA library, resulting in the largest collection of L. stagnalis neuronal transcriptome data currently available. Approximately 42% of the cDNAs can be translated into more than 100 consecutive amino acids, indicating the high quality of the library. The annotated sequences contribute 12% of the predicted transcriptome size of 20,000. Surprisingly, approximately 37% of the L. stagnalis sequences only have a tBLASTx hit in the EST library of another snail species Aplysia californica (A. californica) even using a low stringency e-value cutoff at 0.01. Using the same cutoff, approximately 67% of the cDNAs have a BLAST hit in the NCBI non-redundant protein and nucleotide sequence databases (nr and nt), suggesting that one third of the sequences may be unique to L. stagnalis. Finally, using the same cutoff (0.01), more than half of the cDNA sequences (54%) do not have a hit in nematode, fruitfly or human genome data, suggesting that the L. stagnalis transcriptome is significantly different from these species as well. The cDNA sequences are enriched in the following gene ontology functional categories: protein binding, hydrolase, transferase, and catalytic enzymes.ConclusionThis study provides novel molecular insights into the transcriptome of an important molluscan model organism. Our findings will contribute to functional analyses in neurobiology, and comparative evolutionary biology. The L. stagnalis CNS EST database is available at .

Combinations of binary and tertiary toxic effects of extracts of Euphorbia pulcherima latex powder with other plant derived molluscicides against freshwater vector snails

Molluscicidal activity of different plant moieties in different combinations (binary or tertiary) were tested against freshwater vector snail Lymnaea acuminata and Indoplanorbis exustus in earthen cemented ponds. These snails are belonging to the family Lymnaeidae are known to act as intermediate host of liver fluke Fasciola hepatica cause endemic fascioliasis in cattle and live stock. Binary (1:1) and tertiary (1:1:1) combinations of the rutin, ellagic acid, betulin and taraxerol with Euphorbia pulcherima latex powder were studied molluscicidal activity against freshwater snails Lymnaea acuminata and Indoplanorbis exustus in earthen cemented pond. It was observed that the molluscicidal activity of E. pulcherima latex powder with other plant product in combinations of binary and tertiary against harmful snails Lymnaea acuminata and Indoplanorbis exustus was time as well as dose dependent. There was a significant negative correlation between LC50 values and exposure periods thus increases in exposure time mixed in binary combination (1:1) of the E. pulcherima latex powder with rutin, ellagic acid and taraxerol the LC50 values decreased from 3.19 mg/L (24h)> to 1.82 mg/L (96h); 6.75 mg/L (24h)> to 3.65 mg/L (96h) and 10.33 mg/L (24h)> to 7.37 mg/L (96h) respectively against snail Lymnaea acuminata and E. pulcherima latex powder with rutin, ellagic acid and taraxerol the LC50 values is decreased from 5.91 mg/L (24h)> to 4.0 mg/L (96h); 8.12 mg/L (24h)> to 5.67 mg/L (96h) and 11.94 mg/L (24h)> to 9.48 mg/L (96h) against Indoplanorbis exustus. Same trend of the toxicity was also observed in the molluscicidal activity of E. pulcherima latex with rutin, ellagic acid, taraxerol and betulin in tertiary combinations (1:1:1) against the freshwater snail Lymnaea acuminata and Indoplanorbis exustus.

Molecular Recognition of Neonicotinoid Insecticides: The Determinants of Life or Death

Until the mid-20th century, pest insect control in agriculture relied on largely inorganic and botanical insecticides, which were inadequate. Then, the remarkable insecticidal properties of several organochlorines, organophosphates, methylcarbamates, and pyrethroids were discovered, leading to an arsenal of synthetic organics. The effectiveness of these insecticides, however, diminished over time due to the emergence of resistant insect strains with less sensitive molecular targets in their nervous systems. This created a critical need for a new type of neuroactive insecticide with a different yet highly sensitive target. Nicotine in tobacco extract was for centuries the best available agent to prevent sucking insects from damaging crops, although this alkaloid was hazardous to people and not very effective. The search for unusual structures and optimization revealed a new class of potent insecticides, known as neonicotinoids, which are similar to nicotine in their structure and action as agonists of the nicotinic acetylcholine receptor (nAChR). Fortunately, neonicotinoids are much more toxic to insects than mammals due in large part to differences in their binding site interactions at the corresponding nAChRs. This Account discusses the progress that has been made in defining the structural basis of neonicotinoid and nicotinoid potency and selectivity. The findings are based on comparisons of two acetylcholine binding proteins (AChBPs) with distinct pharmacological profiles that serve as structural surrogates for the extracellular ligand-binding domain of the nAChRs. Saltwater mollusk (Aplysia californica) AChBP has high neonicotinoid sensitivity, whereas freshwater snail (Lymnaea stagnalis) AChBP has low neonicotinoid and high nicotinoid sensitivities, pharmacologies reminiscent of insect and vertebrate nAChR subtypes, respectively. The ligand-receptor interactions for these AChBPs were established by photoaffinity labeling and X-ray crystallography. Both azidopyridinyl neonicotinoid and nicotinoid photoprobes bind in a single conformation with Aplysia AChBP; this is consistent with high-resolution crystal structures. Surprisingly, though, the electronegative nitro or cyano moiety of the neonicotinoid faced in a reversed orientation relative to the cationic nicotinoid functionality. For the Lymnaea AChBP, the azidoneonicotinoid probes modified two distinct and distant sites, while the azidonicotinoid probes, surprisingly, derivatized only one point. This meant that the neonicotinoids have two bound conformations in the vertebrate receptor model, which are completely inverted relative to each other, whereas nicotinoids appear buried in only one conserved conformation. Therefore, the unique binding conformations of nicotinic agonists in these insect and vertebrate receptor homologues define the basis for molecular recognition of neonicotinoid insecticides as the determinants of life or death.

Enzyme inhibition by molluscicidal component of Areca catechu and Carica papaya in the nervous tissue of vector snail Lymnaea acuminata

In the present study toxic effects of active molluscicidal component of Areca catechu and Carica papaya was studied on certain enzymes in the nervous tissue of freshwater snail Lymnaea acuminata. In in vivo and in vitro exposure of arecoline (active component of Areca catechu seed) and papain ( C. papaya latex and seed) significantly inhibited the acetylcholinesterase (AChE), acid and alkaline phosphatase (ACP/ALP) activity in the nervous tissue of L. acuminata. The inhibition kinetics of these enzymes indicate that arecoline and papain caused competitive and uncompetitive inhibition of AChE, respectively, whereas arecoline caused competitive–non-competitive inhibition of ACP/ALP and papain caused non-competitive inhibition of ACP/ALP. Thus the inhibition of AChE, ACP and ALP by arecoline and papain in the nervous tissue of L. acuminata may be the cause of molluscicidal activity of A. catechu and C. papaya, respectively.

Invasive alien freshwater snail species in the Kruger National Park, South Africa

An account is given of all invasive alien freshwater snail species samples found in the Kruger National Park currently on record in the National Freshwater Snail Collection(NFSC) database. This report mainly focuses on samples collected during surveys of selected water bodies in the Kruger National Park (KNP) during 1964, 1995, 2001 and 2006. The progress made by four alien invasive freshwater snail species, Lymnaea columella, Physa acuta, Aplexa marmorata and Tarebia granifera, in colonising water bodies since first being recorded in the KNP is addressed. The results clearly show that all four species are in the process of becoming more widespread than they were when first recorded. However, T. granifera is the only one of these species of which exceptionally dense populations were encountered in several water bodies. All indications are that this species could already have had a negative impact on the species diversity of molluscs in these water bodies, and it is recommended that the situation be closely monitored.

Effect of a toxicant on phagocytosis pathways in the freshwater snail Lymnaea stagnalis

The disturbance of plasma membrane carbohydrates and of lipopolysaccharide (LPS) ligands in relation to cytoskeletal transformations of haemocytes has been investigated after chronic exposure of pond snails (Lymnaea stagnalis) to the peroxidizing toxicant fomesafen. Neither of the two lectins used (concanavalin A and wheat germ agglutinin) showed any binding modification after incubation of the snails in the presence of the toxicant. However, after exposure of the snails to fomesafen, a clear and persistent reduction in LPS labelling of haemocytes occurred. The actin cytoskeleton of the same cells also appeared to be sensitive to the toxicant. The reduction in LPS-binding sites was related to actin staining, leading to the hypothesis that LPS ligands and actin could be similarly modulated by the toxicant. Damaged cells showed non-adherent membrane portions with reduced filopodial extrusions, exhibiting a smooth surface free of microvilli. These changes could lower the spreading and adhesion of the cells and could therefore account for the loss in their phagocytic capabilities.

Viperidae snake venoms block nicotinic acetylcholine receptors and voltage-gated Ca2+ channels in identified neurons of fresh-water snail Lymnaea stagnalis

Viperidae snake venoms block nicotinic acetylcholine receptors and voltage-gated Ca2+ channels in identified neurons of fresh-water snail Lymnaea stagnalis

Ecological modulation of environmental stress: interactions between ultraviolet radiation, epibiotic snail embryos, plants and herbivores

1. The distribution of egg masses of the freshwater snails Lymnaea stagnalis and Planorbarius corneus on the undersides of water lily leaves (e.g. Nuphar lutea) is related to the prevalence of the leaf-mining beetle Galerucella nymphaeae. 2. When given the choice, Planorbarius significantly avoids leaves that were infested by the mining beetle. Conversely, Lymnaea did not discriminate against mined leaves. 3. Intact Nuphar leaves block over 95% of incident ultraviolet radiation. Yet, ultraviolet transmission reaches almost 100% under beetle mining scars. These are several times wider than snail embryos. 4. When exposed to natural sunlight, Lymnaea embryos proved to be resistant to ambient ultraviolet, while Planorbarius embryos were rapidly killed. Thus, one selective advantage of Planorbarius discrimination against mined leaves when depositing its eggs could be the avoidance of ultraviolet radiation passing through mining scars. 5. Other mining-related modifications of the leaves, reduced area, decreased longevity, altered aufwuchs (i.e. biofilm and epibionts) are discussed but seem less relevant for the oviposition preference of Planorbarius. 6. The discriminatory behaviour of this snail species was triggered by water-borne cues emitted by the damaged leaf, not by the eggs or larvae of the beetle. 7. This study illustrates how environmental stress on a given species, ultraviolet radiation in this case, can be ecologically buffered (shading by Nuphar) or enhanced (reduction of Nuphar shading through beetle mining) by associated species. It highlights how the impact of a given stress depends on the identity of the target species as well as on the identity and role of other species in the community.